1. Field of the Invention
The present invention relates to an electromagnetic valve device having a platy armature connected to an end of a valve body for opening and closing a fluid passage, a solenoid device which attracts the armature by attraction force generated when a solenoid coil is energized to allow the valve body to close the fluid passage and releases the armature from the attraction force when the energization is shutoff, and a return spring which thrusts back the armature so that the valve body opens the fluid passage when the energization is shutoff, and a fuel injection apparatus equipped with the electromagnetic valve device.
2. Description of the Related Art
An electromagnetic valve device having a platy armature connected to an end of a poppet valve for opening and closing a fuel passage between a plunger room and fuel spill side, a solenoid device which attracts the armature by attraction force generated when a solenoid coil is energized to allow the poppet valve to close the fuel passage and releases the armature from the attraction force when the energization is shutoff, and a spring which thrusts back the armature so that the poppet valve opens the fluid passage when the energization is shutoff, is widely used in unit injector type fuel injection apparatuses for diesel engines. Fuel injection begins when the armature is attracted by the solenoid device by energizing the solenoid coil and the poppet valve closes the fuel passage to bring the plunger room into closeness, and ends when the armature is thrust back by the spring by shutting off the energization so that the poppet valve opens the fuel passage to allow the plunger room to be communicated with the fuel spill side.
One of such electromagnetic valve device is disclosed in Japanese Laid-Open Patent Application No. 7-279792 (patent literature 1).
This electromagnetic valve device has a platy armature connected to an end of a needle valve for opening and closing a fuel passage between a plunger room and fuel spill side, a solenoid device which attracts the armature by attraction force generated when a solenoid coil is energized to allow the needle valve to close the fuel passage and releases the armature from the attraction force when the energization is shutoff, and a spring which thrusts back the armature so that the needle valve opens the fluid passage when the energization is shutoff. With this valve, fuel injection begins when the armature is attracted by the solenoid device by energizing the solenoid coil and the needle valve closes the fuel passage to bring the plunger room into closeness, and ends when the armature is thrust back by the spring by shutting off the energization so that the needle valve opens the fuel passage to allow the plunger room to be communicated with the fuel feed/spill line.
The electromagnetic valve device is composed such that a damper room is formed by an end face of the solenoid device and an end face of the armature with a small gap between them and an armature room is formed by the other end face of the armature and the inner face of the valve casing, and a communicating passage is provided in the valve casing at a side of the armature to communicate the armature room with the damper room, a check valve being provided in the communication passage so that fluid can flow from the armature room to the damper room and not vice versa.
When the needle valve closes the fuel passage, the check valve is closed by increased pressure in the damper room to bring the damper room into closeness, fuel pressure in the damper room rises to slow down downward velocity of the needle valve to allow the needle valve to sit on the valve seat slowly, and occurrence of bouncing of the needle valve which occurs when the needle valve sit on the valve seat at high speed is prevented.
However, when the needle valve moves up to open the fuel passage, pressure in the armature room rises and pressure in the damper room decreased rapidly, so fluid in the armature room flows into the damper room through the check valve at high velocity. Therefore, cavitation erosion tends to occur on the surface of the armature facing the damper room. Further, as the communication passage and check valve are provided in the valve casing at a side position of the armature, the electromagnetic valve device necessarily becomes large in size to prepare a space for the communication passage and check valve.